1. Field of the Invention
The present invention relates to a speed reducer in a portable electric tool, and particularly to a speed reducer in a portable electric tool for automotive repair, which can increase the torque and prolong the life span in use.
2. Description of Related Art
Referring to FIG. 1, a latest developed portable electric tool is illustrated. The portable electric tool comprises a primary handle 10 and a gearbox on the primary handle. The gearbox is composed of a front casing 21 and a rear casing 22 and a first spacing block 23 and a second spacing black 24 are disposed between the front casing 21 and the rear casing 22.
A motor 30 is fixedly attached to the rear casing 22 and the motor preferably is 12V direct current type for being carried about with the car. A spindle 31 of motor 30 can be inserted between the rear casing 22 and the first spacing block 23. The free end of the spindle 31 provides a motor gear 32 and a first planetary gear set 40 is rotationally provided between the rear casing 22 and the first spacing block 23. The first planetary gear set 40 provides planetary gears 41, 42, 43 surrounding and meshing with the motor gear 32. The respective planetary gears 41, 42, 43 has teeth more than that on the motor gear 32 so as to constitute a first stage of speed reduction. A respective secondary planetary gear 410, 420, 430 is fixed to a respective shaft same as the planetary gears 41, 42, 43 to mesh with a transmission gear 44 for second stage of speed reduction. The transmission gear 44 provides a middle shaft 45 extends through the first spacing block 23 and a driven gear 46 is attached to the middle shaft between the first and the second spacing blocks 23, 24.
A second planetary gear set 50 is arranged between the first and the second spacing blocks 23, 24 and has planetary gears 51, 52, 53 thereon to surround and mesh with the driven gear 46. The planetary gears 51, 52, 53 each provide a pitch diameter and teeth smaller than the driven gear 46 so as to constitute a third stage of speed reduction. Each planetary gear 41, 42, 43 provides a shaft and the respective shaft further has a corresponding secondary gear 510, 520, 530 with a pitch diameter and teeth smaller than the planetary gear 51, 52, 53. A transmission gear 54 is surrounded by and meshing with the secondary gears 510, 520, 530 to constitute a fourth stage of speed reduction. An axial shaft 55 provided on the transmission gear 54 passes through the second spacing block 24 such that a driven gear 56 is arranged on the axial shaft between the second spacing block 24 and the front casing 21.
A third planetary gear set 60 is arranged between the second spacing block 24 and the front casing 21 and has planetary gears 61, 62, 63 surrounding and meshing with the driven gear 56. The teeth and the pitch diameter of respective planetary gear 61, 62, 63 are greater than the driven gear 56 to constitute a fifth stage of speed reduction. Each planetary gear 61, 62, 63 provides a shaft and the respective shaft further has a corresponding secondary gear 610, 620, 630 with teeth smaller than the planetary gear 61, 62, 63. An output gear 71 is surrounded and meshes with the secondary gears 610, 620, 630 to constitute a sixth stage of speed reduction. The output gear 71 has an output shaft 72 extends outward the front casing 21 so that an outer end of the output shaft 72 with an engaging head 73 can fit with sleeve for fastening or loosening bolts or nuts.
The torque provided by the prior art is somewhat insufficient from the point of view with regard to the entire structure of speed reducer thereof. Nevertheless, the most serious disadvantage of the prior art is that the third planetary gear set is easily damaged, and it is the reason that planetary gears 61, 62, 63 are apt to warp outward and become deformed during subjecting the resistant force of output gear 71. Hence, it may occur a problem of planetary gears 61, 62, 63 being in a state of loosening or occur a phenomenon of the output gear 71 or planetary gears 61, 62, 63 becoming slippery during meshing to each other and resulting in a situation of gear fracture. Hence, these defects resided in the prior art have to be overcome from the design of structure.
Accordingly, an object of the present invention is to provide a speed reducer in a portable electric tool, with which an output internal gear with internal circular teeth are arranged to mesh with over pins instead of planetary gears directly. Thus, the output torque can be enhanced and the phenomenon of gear damage or gear loosening can be avoided substantially.